INSIDIOUS Synonyms: 100 Similar and Opposite Words

insidious

adjective

Definition of insidious

as in treacherous

formal causing harm in a way that is gradual or not easily noticed Most people with this insidious disease have no idea that they are infected. an insidious enemy

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Example Sentences

Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of insidious Meanwhile, an insidious supervillain (Kenneth Branagh) lurks, threatening to take Crown down. — Mya Copeland, Variety, 29 July 2026 But there’s a historical, and some might argue insidious, irony to all of this. — Drew Pittock, USA Today, 25 July 2026 But, as Ellis demonstrates in this survey of the city’s racial history, liberal policy achievements tend to obscure more insidious forms of exclusion. — The New Yorker, New Yorker, 20 July 2026 Beneath all the splendor, the couture, the balls, and the opera lurked an undercurrent of hatred, one that would fester and erupt in ways both insidious and catastrophic. — Literary Hub, 17 July 2026 See All Example Sentences for insidious

Recent Examples of Synonyms for insidious

Adjective

And with most of the original cast now long gone, the latest sequel often feels as cursed as that treacherous netherworld.

— Los Angeles Times, Los Angeles Times, 21 Aug. 2026
The first season concludes with the revelation that Mizu’s ambitions of vengeance require her to travel to London — a treacherous journey by sea, as briefly shown in the second season trailer.

— Jess Weatherbed, The Verge, 21 Aug. 2026

Definition of treacherous

Adjective

Clinicians found real value in cases involving subtle fractures in the knees, feet and other extremities, where conventional X-ray findings were inconclusive or missed the fracture altogether.

— Erez Meltzer, Forbes.com, 21 Aug. 2026
Then there are the subtle vanilla notes like those found in Orb Oils’s Lenny fragrance, matcha in Le Labo’s, or, say, Flamingo Estate’s Prinsesstårta roll-on captures notes of marzipan like a slice of Sant Ambroeus Princess cake.

— Arden Fanning Andrews, Vogue, 21 Aug. 2026

Definition of subtle

Adjective

The company alleges trademark infringement, unfair competition and deceptive trade practices.

— Jason St. Angelo, USA Today, 19 Aug. 2026
And, given his high release point, deceptive delivery and deep repertoire, where batters can’t often make good contact.

— Marc Topkin, The Orlando Sentinel, 19 Aug. 2026

Definition of deceptive

Adjective

But to build a web of accusations based on false premises and the manipulation of reality in order to attack the Biennale and a film invited to compete is a petty and unacceptable act.

— John Bleasdale, Variety, 19 Aug. 2026
China’s aircraft engineers have warned that artificial intelligence could feed false data into military intelligence, potentially distorting the design and operation of advanced weapons.

— Aamir Khollam, Interesting Engineering, 19 Aug. 2026

Definition of false

Adjective

That’s misleading, the FTC said, since customers who know how prices are set could take defensive measures, such as using a private browsing session or a virtual private network to mask their browsing history.

— Ashley Belanger, ArsTechnica, 21 Aug. 2026
There are plenty of well-meaning people and experts posting content everyday, but both professors noted that even that material may be misleading, inconclusive or overly generalized.

— Carlos De Loera, Los Angeles Times, 21 Aug. 2026

Definition of misleading

Adjective

Bogus texts, mystery calls, deceitful emails all aimed at stealing your personal information and your money are relentless.

— Donna Vickroy, Chicago Tribune, 13 Aug. 2026
The mutual trust and goodwill that xenia sought to cultivate has been eroded by this one deceitful act, creating a world that is defined by this moral violation.

— Brianna Zigler, Entertainment Weekly, 19 July 2026

Definition of deceitful

Adjective

When requirements are unclear, AI may make incorrect assumptions that compound over multiple iterations.

— Son Nguyen, Forbes.com, 18 Aug. 2026
The senators also noted that grants were canceled out of the blue with form letters, which had contradictory explanations and incorrect citations.

— Beth Mole, ArsTechnica, 18 Aug. 2026

Definition of incorrect

Browse Nearby Words

inside tracks

insidious

insidiously

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Style

“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 25 Aug. 2026.

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Synonyms of insidious

adjective

Example Sentences

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